I have no clue why the isolated tests fail, tried to debug the CI but can't get it to display more information... will try again later

That was the weirdest bug I've ever seen. When trying to use the same environment as the CI, I had to install deps in the packages/process directory.

Doing so made a new error appear on the ProcessPoolResults class: I had to implement serialize and unserialize, I still don't know why. The class implemented our ArrayInterface interface, which in turn implements Iterator, ArrayAccess and Countable.

As far as I know, none of them implement Serializable, so I'm clueless. I implemented these three interfaces directly instead of going through ArrayInterface and the error disappeared? Even though it's namespaced, I'm assuming there is a resolution issue with the interface name "ArrayInterface".